A diminution of the quantity of tears produced and distributed through the lachrymal ducts or a decrease in the stability of the tear film produced results in a condition of the eye commonly referred to as dry eye or dry eye syndrome. Dry eye is a condition of the eye that usually causes a feeling of discomfort such as ocular dryness, grittiness, burning, soreness or scratching, depending upon the condition of the subject. Many theories have been offered to explain the possible causes of dry eye syndrome including insufficient tear volume, mucous deficiency, evaporative losses from tear film and the inability to produce an adequate tear film. Dry eye syndrome, if allowed to remain untreated and uncorrected, can result in permanent damage to the eye with degradation of the exposed ocular tissues or a breakdown of the corneal tissue necessitating, in extreme cases, corneal transplants. Proposed causes for dry eye syndrome, treatment and symptoms thereof are all described in detail in "The Preocular Tear Film In Health, Disease and Contact Lens Wear", The Dry Eye Institute, Lubbock, Tex., 1986.
The most common treatment for dry eye syndrome involves the alleviation of the symptoms by topical administration of a teas substitute that adds a volume of liquid to the anterior surface of the eye and related adnexa. Typical tear substitute compositions comprise water soluble, aqueous polymer compositions. Examples of such compositions include saline solutions of polyvinyl alcohols, hydroxypropyl methylcellulose or carboxymethylcelluloses. Formulations containing substituted cellulose ethers and hydrophilic polymers impart viscosity to the tear formulation and are currently in use for the treatment of dry eye syndrome.
Compositions used in the treatment of dry eye syndrome typically contain a preservative such as benzalkonium chloride if they are intended for multiple use. Preservative free formulations are known in the art. Such preparations are packaged in unit dose containers which are sterile in the unopened form. However, because of the absence of a preservative, each unit dose must be immediately discarded after the prescribed dose has been instilled into the eye. If the opened container is retained for repeated use, microbial contamination can occur which upon administration to the ocular surface increases the risk of infection. Although the use of preservative agents in formulations for treating conditions such as dry eye syndrome results in the destruction or inhibition of the growth of micro-organisms, their use can also damage the ocular tissue. The toxic effects of preservatives is even more pronounced where chronic treatment is required such as in the treatment of dry eye or glaucoma.
There is a need, therefore, for a preservative free composition for the treatment of conditions of the eye which can be used for multiple dose application without the fear of microbial contamination.
It is an object of the present invention to provide an ophthalmic formulation which can be used as a wetting agent for the treatment conditions of the eye such as of dry eye syndrome.
It is another object of the present invention to provide a preservative-free ophthalmic composition which can be used as a carrier for ophthalmic medicaments for the alleviation of the symptoms of dry eye which is not susceptible to contamination by micro-organisms.
A further object of the invention is to provide a preservative-free ophthalmic composition suitable for multi-dose administration.